The art disclosed by the present specification relates to a current sensor suited to measure an output current of a switching circuit, and an electric power converter that includes such a current sensor. The current sensor disclosed by the present specification utilizes a magneto-optical element (magneto-optical crystal).
A current sensor employing a magneto-optical element is an example of devices for accurately measuring a current within an extremely short time. The current sensor is basically constituted of the magneto-optical element that is arranged at a current measurement point, a laser light source that irradiates the magneto-optical element with a laser, a laser receiver that receives a laser reflected by (or a laser transmitted through) the magneto-optical element, and a calculation unit that calculates a value of the current at the measurement point from a polarization state of the received laser.
The magneto-optical element has the specification of changing the polarization state of reflected light or transmitted light in accordance with the received magnetic field. Accordingly, the magneto-optical element is arranged within the magnetic field generated by the current, and a laser is radiated onto the magneto-optical element, so that the magnitude of the current can be obtained from the polarization state of reflected light (or transmitted light). The current sensor employing the magneto-optical element has the advantages of being able to carry out a measurement within an extremely short time (having a wide frequency band), being noninvasive, being resistant to electromagnetic noise, etc. Incidentally, the phenomenon of rotation of the plane of polarization resulting from changes in the polarization state of transmitted light due to the influence of a magnetic field is referred to as a Faraday effect, and the phenomenon of changes in the polarization state of reflected light is referred to as a magneto-optical Kerr effect.
For example, an application example of such a current sensor is disclosed in Japanese Patent Application Publication No. 6-224727 (JP-6-224727 A) (Patent Document 1). Besides, an example of such a current sensor is disclosed in Japanese Patent Application No. 2011-56473 (which had not been laid open when the present application was filed) as well. In particular, Patent Document 1 proposes the application of a current sensor employing the foregoing magneto-optical element as a current sensor that measures an output alternating current of an inverter, for the reason that the inverter of an electric vehicle or a railroad vehicle generates a strong electromagnetic noise.
A switching operation constitutes one cause of an electromagnetic noise not only in an inverter but also in an electric power converter including a switching circuit. The art disclosed by the present specification also adopts a current sensor that utilizes a magneto-optical element. The art disclosed by the present specification takes advantage of the configuration specific to the switching circuit, and suppresses the influence of a noise resulting from the switching operation in measuring the current.
In many cases, a signal for driving a switching circuit is a PWM signal (or a PAM signal). The PWM signal is generated from a periodic signal referred to as a carrier signal and a signal referred to as a command signal (a drive signal). The command signal is equivalent to an alternating current waveform that is desired to be output. A controller for the switching circuit compares the carrier signal and the command signal with each other, and generates a variable pulse width signal whose pulse width corresponds to a period in which the voltage of one of the signals (e.g., the carrier signal) is high, namely, a PWM signal. It should be noted herein that the timing when a switching operation is performed is equivalent to an intersecting point of the carrier signal and the command signal. Then, a noise is generated as a result of the switching operation. Thus, the art disclosed by the present specification adjusts the timing for emitting a laser in such a manner as to avoid the intersecting point. Concretely, in a current sensor disclosed by the present specification, a laser light source radiates light in synchronization with a carrier signal for generating a drive signal for the switching circuit. Due to this configuration, laser light for measuring the current is radiated at timings other than the timing of the switching operation. A noise generated at the switching timing has no influence or, if any, a little influence on the measured value of the current based on such laser light.
In order to generate a pulsed laser that is synchronized with the carrier signal, for example, it is appropriate to compare the command signal with a constant voltage level and the carrier signal with each other, and radiate the laser only for a period in which the carrier signal is large (or only for a period in which the carrier signal is small). The pulsed laser for radiating the laser during the period in which the carrier signal is large is a pulsed laser that is synchronized with the peak of the carrier signal, and moreover, is a pulsed laser around the peak. On the contrary, the pulsed laser for radiating the laser during the period in which the carrier signal is small is a pulsed laser that is synchronized with the bottom of the carrier signal, and moreover, is a pulsed laser around the bottom. The use of such a pulsed laser makes it possible to measure a current except at the switching timing, and to exclude the influence of a noise resulting from switching.
Incidentally, the foregoing advantages can be obtained if the pulsed laser is triggered in the neighborhood of the peak or bottom of the carrier signal. It should therefore be noted that, for example, a laser light source that compares command vibrations at a level close to the peak (or the bottom) and a carrier signal with each other and generates a pulse only for a predetermined width of time from the timing of their intersecting point is also useful.
There are also other advantages of utilizing the carrier signal. Since the existing carrier signal is utilized, there is no need to separately prepare a periodical trigger signal for generating the pulsed laser. By using the pulsed laser instead of a continuous wave laser, the service life of the laser light source is prolonged. Besides, the heating value of the pulsed laser is smaller than the heating value of the continuous wave laser. In the case where the current sensor is used to measure alternating currents in three phases of the inverter, three alternating current signals can be measured at the same timing by generating three pulsed lasers on the basis of a single carrier signal.
The foregoing current sensor constitutes an art utilizing the properties of the switching circuit. Therefore, an electric power converter that is equipped with the foregoing current sensor and the foregoing switching circuit is also a novel device disclosed by the present specification. In particular, an inverter that is equipped with a current sensor that measures three output alternating currents, namely, a U-phase output alternating current, a V-phase output alternating current, and a W-phase output alternating current by three laser light sources that are synchronized with a single carrier signal is the most typical example of the novel device disclosed by the present specification.
The details of the art disclosed by the present specification and further improvements in this art will be described in the mode of carrying out the invention.
A current sensor according to an embodiment of the invention will be described with reference to the drawings. In the present embodiment of the invention, the current sensor is applied to an inverter for driving a motor of a hybrid vehicle. The inverter is equipped with the current sensor in order to measure three output currents of the inverter, namely, a U-phase output current, a V-phase output current, and a W-phase output current.
An electric power for driving the motor 8 is supplied from a main battery 3. The main battery 3 has an output voltage of, for example, 300 V. Incidentally, although not shown in the drawing, the hybrid vehicle 2 is equipped with an auxiliary battery for supplying electric power to a group of devices (generally referred to as “auxiliaries”) that are driven at a voltage lower than the output voltage of the main battery 3, such as a car navigation system, a room lamp and the like, as well as the main battery 3. The auxiliary battery has an output voltage (i.e., a voltage for driving the auxiliaries) of, for example, 12 V or 24 V. The appellation “main battery” is used for the sake of convenience, in order to make a distinction from “auxiliary battery”.
The main battery 3 is connected to an inverter 5 via a system main relay 4. The system main relay 4 is a switch that connects/disconnects the main battery 3 and an electric power circuit of the vehicle to/from each other. The system main relay 4 is changed over by a superordinate controller (not shown).
The inverter 5 includes a voltage converter circuit 12 that steps up the voltage of the main battery 3 to a voltage (e.g., 600 V) suited to drive the motor, and an inverter circuit 13 that converts a direct-current electric power obtained after the stepping up of the voltage into an alternating current. An output current of the inverter circuit 13 is equivalent to an electric power supplied to the motor 8. Incidentally, the hybrid vehicle 2 can also generate electricity by the motor 8, through the use of a driving force of the engine 6 or deceleration energy of the vehicle. In the case where the motor 8 generates electricity, the inverter circuit 13 converts an alternating current into a direct current, and furthermore, the voltage converter circuit 12 steps down the voltage to a voltage slightly higher than that of the main battery 3, and supplies the voltage to the main battery 3. Both the voltage converter circuit 12 and the inverter circuit 13 are circuits that are mainly constituted of switching circuits 14 such as IGBT's and the like. A controller 20 (an inverter controller) generates and supplies a control signal (a PWM signal) to each of the switching circuits 14. Incidentally, each of the switching circuits 14 is configured, concretely, by connecting an IGBT and a diode to each other in an anti-parallel manner, and the PWM signal is supplied to a gate of the IGBT. Besides, it should be noted that although the inverter 5 is equipped with a plurality of switching circuits in each of the voltage converter circuit 12 and the inverter circuit 13, only one of the switching circuits is denoted by the symbol “14” in
The controller 20 includes a carrier signal generator 21 and a PWM generator 22. The carrier signal generator 21 generates triangular waves of a predetermined frequency. The PWM generator 22 compares a motor command signal (a motor drive signal) transmitted from the superordinate controller (not shown) and a carrier signal with each other, and generates a pulse signal (i.e., a PWM signal) that has, as a pulse width, a period in which the voltage of the carrier signal is higher than the voltage of the motor command signal. The controller 20 generates a PWM signal individually for each of the switching circuits. The generated PWM signal is supplied to each of the switching circuits of the inverter circuit 13.
It should be noted that although the inverter circuit 13 is equipped with the plurality of the switching circuits, there is one carrier signal.
A capacitor C2 is connected to a low-voltage side (i.e., a main battery side) of the voltage converter circuit 12, and a capacitor C1 is connected to a high-voltage side (i.e., an inverter circuit side) of the voltage converter circuit 12. The capacitor C2 is connected in parallel to the voltage converter circuit 12, and the capacitor C1 is also connected in parallel to the voltage converter circuit 12. The capacitor C2 constitutes a step-up/step-down circuit together with a reactor L1 and the switching circuits. The capacitor C2 temporarily accumulates the electric power of the main battery 3, and serves as an electric power source when the reactor L1 generates an induced electromotive force. The capacitor C2 is sometimes referred to as a filter capacitor. The capacitor C1 is inserted to smooth the current input to the inverter circuit 13, and is sometimes referred to as a smoothing capacitor. Incidentally, an electric wire on a high-potential side of a group of switching elements of the inverter circuit 13 is referred to as a P line, and an electric wire on a ground potential side of the group of the switching elements of the inverter circuit 13 is referred to as an N line. The capacitor C1 is inserted between the P line and the N line. Since a large current is supplied from the main battery 3 to the motor 8, both the capacitor C2 and the capacitor C1 are large in capacity.
In order to control the current supplied to the motor 8, the inverter 5 performs current feedback control. Thus, the inverter 5 is equipped with a current sensor 30. The current sensor 30 is constituted of a controller 31 (a sensor controller) and three sensor bodies 32. The controller 31 receives a carrier signal from a carrier signal generator 21 in the inverter controller 20, and generates a laser drive signal that is synchronized with the carrier signal. The laser drive signal is a pulse signal that is synchronized with the carrier signal. The laser drive signal is transmitted to each of the three sensor bodies 32. Each of the sensor bodies 32 irradiates a target with a pulsed laser on the basis of the laser drive signal, and receives reflected waves thereof. The target is a magneto-optical element that is installed in a current cable. Each of the sensor bodies 32 transmits a signal indicating a polarization angle of the laser reflected waves to the controller 31. The controller 31 specifies the magnitude of the current on the basis of signals transmitted from the sensor bodies 32. As shown in
The configuration of each of the sensor bodies 32 will be described.
The laser light source 41 radiates a pulsed laser that is synchronized with a carrier signal of the inverter 5. The advantage of such radiation will be described.
On the other hand, the controller 31 of the current sensor 30 generates a laser drive signal from the carrier signal Ca and a reference signal Dd with a constant voltage level (see
The inverter 5 is equipped with the three sensor bodies 32 that measure three output currents, namely, a U-phase output current, a V-phase output current, and a W-phase output current respectively. The laser drive signal supplied to all the sensor bodies is based on the single carrier signal Ca. Therefore, the inverter 5 can simultaneously measure three output currents, namely, a U-phase output current, a V-phase output current, and a W-phase output current.
In the example of
The points to remember about the art disclosed by the embodiment of the invention will be described. As shown in
Other advantages of the current sensor 30 will be described. The laser light source 41 radiates a pulsed laser, and hence has a longer service life than in the case of a continuous wave laser. Besides, the laser light source 41 radiates a pulsed laser, and hence has a smaller heating value than in the case of a continuous wave laser.
In the embodiment of the invention, the current sensor that measures the output currents of the inverter has been described. The art disclosed by the present specification is characterized in that a pulsed laser is radiated at timings other than the switching timing. The art disclosed by the present specification is not limited to inverters, but is widely applicable to electric power converters having switching circuits. For example, in the inverter 5 shown in
The representative and nonrestrictive concrete examples of the invention have been described in detail with reference to the drawings. This detailed description is simply intended to inform those skilled in the art of the details for carrying out the preferred examples of the invention, and is not intended to limit the scope of the invention. Besides, the additional features and inventions disclosed herein can be used independently of or in combination with other features and inventions, in order to provide a further improved current sensor and a further improved electric power converter.
Besides, the combination of the features and processes disclosed in the foregoing detailed description is not indispensable in carrying out the invention in a broadest sense, but is mentioned merely for the purpose of describing the representative concrete examples of the invention in particular. Furthermore, the various features of the foregoing representative concrete examples and the various features of what is set forth in the independent and dependent claims should not necessarily be combined in accordance with the concrete examples mentioned herein or according to the sequence of citation, in providing any additional and useful embodiment of the invention.
All the features described in the present specification and/or the claims are intended to be disclosed individually or independently of one another as restrictions on the disclosure upon the filing of the application and the specific matters set forth in the claims, apart from the configuration of the features described in the embodiment of the invention and/or the claims. Furthermore, all the numerical ranges and groups or assemblages are described with the intention of disclosing a configuration in between, as restrictions on the disclosure upon the filing of the application and the specific matters set forth in the claims.
The concrete examples of the invention have been described above in detail, but these are nothing more than exemplifications, and do not limit the claims. The art set forth in the claims encompasses various modifications and alterations of the concrete examples exemplified above. Besides, the technical elements described in the present specification or the drawings are technically useful alone or in various combinations, and are not limited to the combination set forth in the claims at the time of the filing of the application. Besides, the art exemplified in the present specification or the drawings achieves a plurality of objects at the same time, and is technically useful by achieving one of the objects alone.
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/JP2012/054426 | 2/23/2012 | WO | 00 | 8/8/2014 |